Method for the production of zein textile fibers



Dec. 11, 1962 H, 5- MQRGANY JR 3,068,06

METHOD FOR THE PRODUCTION OF' ZEIN TEXTILE FIBERS Filed July 25, 1960 ATTORNEY United States Patent O 3,068,062 METHOD FOR THE PRODUCTION F ZEIN TEXTILE FIBERS Herbert S. Morgan, Jr., Decatur, Ala., assignor, by mesne assignments, to Monsanto Chemical Company, a corporation of Delaware Filed July 25, 1960, Ser. No. 45,066 6 Claims. (Cl. 18-54) This invention relates to the production of synthetic textile filament and fiber. More particularly, the invention relates to the production of improved synthetic textile fiber and filament from vegetable protein materials, suchl `as the prolamines, and especially zein and the like.

Synthetic textile fibers and filaments prepared from the prolamines and particularly Zein are well-known. Furthermore, methods for the production of such textile fibers and filaments have been the subject of a great deal of research which has resulted in various processes. A number these processes have been employed in industrial installations in the past. However, none of the processes heretofore known result in the production of protein fibers of laments, having a desired tensile strength or tenacity in either a wet or dry state although commercially acceptable fibers and filaments have been produced. Among the other drawbacks of protein fibers and filaments produced by known processes are the inability to withstand bleaching without loss of physical strength and appearance and the inability to withstand acid dyeing at high temperatures. yFibers and filaments produced according to known procedures which have good dyeability possess inferior tenacity and chemical resistance to bleaches. On the other hand, where the tenacity is improved inferior dyeability results. These inferior properties are partially overcome by the teaching in U.S. Patent 2,845,362 to H. S. Jenkins, et al., which discloses a zein textile fiber having acceptable chemical resistance, dyeability and tenacity. However, even lthe improved tenacity obtained according to the teaching of this patent although it falls vWithin acceptable limits does not meet the most desirable qualifications of tenacity. Consequently, there exists a need for a textile fiber prepared from prolamines such as zein which has improved tenacity in both wet and dry states but still exhibits good dyeability and chemical resistance.

Accordingly, it is a primary object of this invention to provide a method for the production of prolamine textile fibers and filaments having high tensile strength. It is another object of the invention to provide a method for the production of prolamine textile bers and filaments having good dyeability and chemical resistance. Still another object of the invention is to provide a method for the production of prolamine textile `fibers and filaments having good elongation characteristics during hotwet conditions of textile processing. Another object of the invention is to provide a continuous wet spinning method for the production of prolamine textile fibers and filaments. Other objects and advantages of the invention will be apparent from the following description.

The accompanying fiowsheet illustrates the new method of this invention.

Referring to the flowsheet, it Will be seen that the new method of preparation of prolamine fibers and filaments comprises seven major steps: solution preparation, deaeration, spinning, saturation, stretching, resaturation and postcure, all of which are important in order to obtain a textile fiber or filament having the desirable tenacity, dyeability, chemical resistance and elongation. However, it has now been found that solution preparation, saturation steps and cascade streching in particular salt solutions have a critical effect on the tenacity while at the same time dyeability, chemical resistance and the like are not adsolution. Solutions containing from 18.0 to 20.0 percent lee versely affected. Furthermore, the beneficial effects derived from the practice of the present invention extend to fibers and filaments of widely varying denier, that is. from a denier per filament of about 0.5 to 200.0.

In general the process of this invention may be described as follows. An aqueous prolamine solution is prepared in accordance with the prior art by dissolving Zein in a mixed solvent containing sodium hydroxide, one or more water-soluble ionizable salts and formaldehyde or a formaldehyde producing compound. Zein raw material having an alkali gel time of 25 to 40 minutes is preferred. By alkali gel time is meant the time in minutes required, by heating at 45 C., for an aqueous zein dispersion containing 2.5 percent by weight of sodium hydroxide and 16 percent by weight of Zein raw material to reach a viscosity of poises at 45.0 C. as measured by the Brookfield viscometer at l r.p.m.

A dispersion of zein of from about 15 percent to about 22 percent by weight is prepared by slurrying the Zein in water -at .a temperature of about 15 C. to 30 C., preferably about 25 C. To ythis slurry are added from about .01 percent to about 2.5 percent of one or more watersoluble ionizable salts and from 1.2 percent to 2.0 percent sodium hydroxide, the percentages of sodium hydroxide and .salt being based on the Zein content by weight. The alkali is added slowly with stirring until the Zein is cornpletely dissolved. The solution is stirred for l0- to 25 minutes at 20 C. to 25 C. to insure complete dissolution. When the viscosity 4of the solution measured on a Brookfield Viscometer at l r.p.m. and 25 C. reaches a point in .the range 5 to 2000 poises and preferably in the range of to 500 poises, formaldehyde is added thereto in the form of a 37 percent formalin solution or as polyoxymethylene in equivalent amount.

The amount of formaldehyde added at this point is` The solution -is'spun using conventional wet spinning equipment. The spinning viscosity may range from 60 to 25,000 'poises at 25 C. measured at 1 r.p.m. on the Brookfield viscometer.

It will be obvious to those skilled in the art that the steps in preparing the Zein solution may be varied chronologically and .that the amounts of each constituent employed can be varied Within certain limitations. However, in order to prepare a solution which permits spinning of the new improved filaments and films according Vto the process of this invention, the total solids content of any solution should not be less than 15.0 percent nor more than 22.0 percent, based on the total weight of the solids,-based on the total weight of the solution, are preferred.

The water soluble ionizable salts mentioned hereinabove are employed in an amount of 0.01 to 2.00 percent, based on the weight of the zein. The preferred amount is from 0.10 to 0.50 percent. Typical examples of water soluble Yionizable salts are sodium sulfide, sodium sulfate, ammonium sulfate, sodium sulfite, sodium chloride-calcium chloride, aluminum sulfate, sodium bisul-fite, ammonium chloride, sodium thioglycolate .and .the like. The optimum amount of any salt varies with the particular system, that is, the character of the zein, the concentration of sodium hydroxide in the Zein solution, and the concentration of formaldehyde in the Zein solution.

The mixture is then stirreduntil a smooth homogeneous solution results at which time it is deaerated under reduced pressure prior to spinning.

The coagulation bath is one that is normally used in the art. It consists essentially of an acidic solution comprising water, sulfuric acid, sodium sulfate, formaldehyde, which leaches into the bath from the spin solution, and hydrated colloidal silica.

The sulfuric acid content of the coagulating bath is maintained within the range from 3.0 percent to 15.0 percent by weight and preferably at 11.0 percent. The sodium sulfate concentration of the coagulating bath may vary within the range from percent to 2.0 percent by weight and preferably at about 1.0 percent. The concentration of formaldehyde which tends to leach out of the spin solution and to build up in the coagulating bath should not rise above 1.0 percent by weight. A higher concentration of formaldehyde interferes with the coagulation process. The hydrated silica content of the coagulating bath is maintained within the range from 1 percent to 3 percent by weight and preferably at 2.5 percent. It acts as an anti-plastering agent to prevent sticking of the filaments due to heat and pressure when the filaments are in a plastic state after coagulation.

The temperature of the coagulation bath is maintained within the range of from about 20 C. to 30 C. and preferably at about 25.0 C. This range improves and facilitates the coagulation process since no special heating or cooling means are necessary for maintaining a close temperature control as taught by the prior art in order to obtain zein fibers of improved tensile strength and tenacity.

The coagulation time, i.e., the length of time that the spun liber is maintained in the coagulation bath, is preferably indicated by a spinning speed of 15.7 feet per minute with the spinneret submerged to a depth of 10.0 inches in the coagulation bath. The coagulation time may vary as much as 50 percent from the time corresponding to the figures given above.

After stretching in the coagulation bath the fiber is immediately saturated to effect partial dehydration. This saturation process requires from 0.5 to 5.0 minutes depending upon the speed of operation. The saturation solution may contain from 3 to 15 percent sulfuric acid by weight and preferably percent, and from 2 to 10 percent formaldehyde by weight and preferably 5.0 percent. The solution is saturated with sodium chloride and is maintained at a temperature of from 25 to 80 C. and preferably 50 C. These percentages may vary according to the spinning speed and size of filament tow employed. At this stage in the description of the process of the invention it should be pointed out that no precuring is necessary. The prior art teaches that in the production of high tenacity zein fibers precuring must carried out after the fiber tow leaves the coagulation bath and prior to the stretchingroperation. The improved process of this inven-Y tion eliminates the time and expense involved in the precuring operation.

After saturation the zein fiber is immediately stretched in a suitable stretch media, for example, a saturated salt solution, water, or polyethylene glycol at a temperature of from 25 to 116 C., depending upon the media employed. The preferred media is a saturated ammonium sulfate solution at a temperature of from 100 to 110 C. A cascade stretch of 5.33 produced the best tensile properties. The stretch solution may also contain small amounts of sulfuric acid, sodium sulfate, formaldehyde and silica carried into the stretch bath with the tow.

The fiber is then resaturated and postcured in accordance with the prior art. The fiber remains in the saturator long enough to effect complete saturation of the fiber with the postcuring solution and complete replacement of the water and loosely held chemicals in the liber as it comes from the stretching operation. The postcuring solution usually is a water solution containing from 4 to 7 percent sulfuric acid by weight and preferably 5 percent, 0.5 to 1 percent formaldehyde by weight and preferably 0.75 percent, and is saturated with sodium chloride.

The temperature of the postcuring solution is maintained within the range from 50 C. to 70 C. and preferably 60 C.

The postcure treatment usually consists of subjecting the fiber tow to a temperature of from 43 to 52 C., preferably 44.5 C., for a period 115 to 125 minutes, preferably 1120 minutes in an atmosphere of air at a relative humidity of to 100%.

vOther treatments may follow the postcuring treatment such as washing, drying, baking, bleaching, finishing and the like.

The fibers of this invention have improved properties not heretofore shown in any protein fibers. These fibers not only have a circular cross-section which is clear,

transparent and completely free of any opaque, striated portions but also these fibers have a high tenacity with a dry modulus of 48 grams per denier. The degree of orientation is significantly higher than any obtained in the prior art teachings as indicated by a specific birefringence index of 13.4 103 and an X-ray orientation ratio of 1.93. Physical and chemical stability to conditions of textile processing such as changes in temperature and moisture conditions as shown by Table I is characteristic of the improved fibers of this invention.

It has also been found that maintaining the fiber under just enough tension to prevent relaxation, preferably suliicient tension to maintain a degree of stretch of from 3 to 7 percent and preferably 5 percent during the steps of washing, drying and baking improves and increases the strength of the fibers. In prior commercial practice zein fibers were relaxed during such processing.

The new and improved process of the invention may be illustrated by the following examples of the preferred method of the invention.

EXAMPLE I A zein dope was prepared by slurrying 841.3 grams of Zein A (Corn Products Refining Co.) in 2874.9 grams of distilled water at 25 C. and to the slurry was added 0.8 gram of ammonium chloride with stirring. An alkali solution containing 13.3 grams of sodium hydroxide and 6.1 grams of hydrous sodium sulfide dissolved in 242.0 grams of water was added slowly over a 30 minute period to dissolve the protein. The solution was stirred for 18 minutes at 20 C. and the viscosity at the end of the stir cycle was poises at 30 C. At this point 21.6 gramsof neutral 37 percent formalin was added and the mixture stirred for ten minutes until smooth.

The dope was deaerated in anlnternational centrifuge and spun with a 1,000 hole 3 mil platinum jet using conventional wet spinning equipment. The dope was coagulated in a solution bath containing 11.0 percent sulfuric acid, 1.2 percent sodium sulfate and 2.5 percent silica at 25 C. After stretching in the spin bath at a 2.0 jet stretch, the freshly spun tow was immediately saturated for 5.0 minutes at 50 C. in an aqueous saturated salt solution containing 10 percent sulfuric acid, 5.0 percent formaldehyde and small amounts of salt added periodically to maintain complete salt saturation. The tow was immediately stretched to a maximum cascade stretch of 5.33 in a saturated ammonium sulfate solution at 106 C., resaturated at 60 C. in a aqueous saturated salt solution containing 5.0 percent sulfuric acid, 0.75 percent formaldehyde and excess salt added as needed to maintain complete salt saturation.

The stabilized tow was postcured, then relaxed, washed, air dried and baked for 45 minutes at 150 C.

The resulting fiber had the following properties:

Size of filament denier 0.85 Dry tenacity gm/denier-- 2.17 Dry elongation percent 13 Dry modulus gm/denier 48 Yield point gni/denier..- 1.25 Breaking toughness gm./denier 0.22 Boil shrinkage (3v min.) -percent-- 10 Dry heat shrinkage:

at C 263 at C 277 30% at C 287 Specific birefringence index 13.4 10*3 X-ray orientation ratio 1.93

The table below shows further test results on the fibers obtained from Example I. These results were obtained from an yaverage of 20 filament breaks with the Instron Tensile Tester for the 0.85 and 0.94 denier per filament bers and from an average of 10 bundle breaks using the Scott IP4 Tester for the 1.87 denier filaments.

Zein fibers were prepared as in Example I except that the fibers were stretched 5 percent and maintained under sufficient tension to hold this degree of stretch during washing, drying Iand baking. The bers of 0.77 denier had an average dry tenacity at 70" F. of 2.24 grams per denier with individual filament breaks as high as 3.08 grams per denier. The tenacity was obtained from an Iaverage of 10 filament breaks with the Instron Tensile Tester.

The data included herein clearly indicate that the improved process of this invention makes possible the production of prolamine fibers of the highest quality with respect to tenacity, chemical :resistance and other desirable features.

As many variations of this invention may be made without departing from the spirit and scope thereof it is intended that the invention be Hunted solely by the scope of the appended claims.

-I claim:

11. A process for the production of zein fibers comprising dissolving zein in an aqueous alkaline solution, extruding the resulting solution into an acidic coagulation bath, saturating the resulting tber immediately after coagulation with an aqueous saturation solution containing from 3 to 15 percent by weight of sulfuric acid, from 2 to 10 percent by weight of formaldehyde and saturated sodium chloride at a temperature of from to 80 C. for a period of time of up to 5 minutes, stretching the fiber in a saturated salt solution at a temperature of from 25 to 116 C. sufficiently to maintain a cascade stretch of from 3 to 6.0, resaturating the ber in an aqueous resaturation solution containing 3 to 10 percent sulfuric acid and from about 3 to 10 percent formaldehyde yand which is at least 90 percent saturated with sodium chloride, and dry postcuring the fiber at a temperature of from 43 to 52 C. for a period of from 115 to 125 minutes in air having a relative humidity of 95 to 100 percent.

2. A process for the production of zein fibers comprising dissolving from l5 to 22 percent by weight of zein in an aqueous alkaline solution, eXtruding the resulting solution into an acidic coagulating bath at a temperature of from about 20 to 30 C., saturating the resulting fiber immediately after coagulation with an aqueous saturation solution containing from 3 to 15 percent by weight of sulfuric acid, from 2 to 10 percent by weight of formaldehyde and saturated sodium chloride at a temperature of from 25 to 80 C. for a period of time of up to 5 minutes, stetching the ber in a saturated salt solution at a temperature of from 25 to 116 C. suiiiciently to maintain a cascade stretch of from 3 to 6.0, resaturating the fiber in an aqueous resaturation solution containing 3 to 10 percent sulfuric acid and from about 3 to 10 percent formaldehyde and which is at least percent saturated with sodium chloride, and postcuring the fiber at a temperature of from 43 to 52 C. for a period of from 115 to 125 minutes in air having a relative humidity of 95 to percent.

3. The process defined in claim 2 wherein the saturated sal-t solution is a saturated solution of ammonium sulfate at a temperature of from 100 to 110 C.

4. In a process for the production of zein fibers, the steps of spinning a zein solution into an acidic coagulating bath at a temperature of from about 20 to about 30 C., saturating the resultant zein fiber immediately after coagulating with an aqueous saturation solution containing from 3 -to 15 percent by weight of sulfuric acid, from 2 to 10 percent by weight of formaldehyde and saturated sodium chloride at a temperature of from 25 to 80 C. for a period of time up to to 5 minutes, stretching the ber in a saturated salt solution at a ytemperature of from 25 to 116 C. suiiiciently to maintain a cascade stretch of up to 6.0, and resaturating with an aqueous resaturation solution containing 3 to 10 percent sulfuric acid and from about 3 to 10 percent formaldehyde and which is at least 90 percent saturated with sodium chloride.

5. The process defined in claim 4 wherein the saturated salt solution is a saturated solution of ammonium sulfate at a temperature of 100 to 110 C.

6. In a process for the production of zein fibers, the steps of spinning a zein solution comprising 18 to 20 percent zein by weight into an `acidic coagulating bath at a temperature of 25 C., saturating the resultant zein fiber immediately after coagulation with an aqueous saturation solution containing from 3 to l5 percent by weight of sulfuric acid, from 2 to 10 percent by weight of formaldehyde and saturated sodium chloride at a temperature of from 25 to 80 C. for a period of time of up to 5 minutes, stretching the ber in a saturated salt solution at a temperature of from 25 to 116 C. sufficiently to maintain a cascade stretch of up to 6.0 and resaturating with an aqueous resaturation solution containing 3 to 10 percent sulfuric acid and from about 3 to 10 percent formaldehyde and which is at least 90 percent saturated with sodium chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,864,663 Lis Dec. 16, 1958 

4. IN A PROCESS FOR THE PRODUCTION OF ZEIN FIBERS, THE STEPS OF SPINNING A ZEIN SOLUTION INTO AN ACIDIC COAGULATING BATH AT A TEMPERATURE OF FROM ABOUT 20 TO ABOUT 30* C., SATURATING THE RESULTANT ZEIN FIBER IMMEDIATELY AFTER COAGULATING WITH AN AQUEOUS SATURATION SOLUTION CONTAINING FROM 3 TO 15 PERCENT BY WEIGHT OF SULFURIC ACID, FROM 2 TO 10 PERCENT BY WEIGHT OF FORMALDEHYDE AND SATURATED SODIUM CHLORIDE AT A TEMPERATURE OF FROM 25 TO 80* C. FOR A PERIOD OF TIME UP TO 5 MINUTES, STRETCHING THE FIBER IN A SATURATED SALT SOLUTION AT A TEMPERATURE OF FROM 25 TO 116* C. SUFFICIENTLY TO MAINTAIN A CASCADE STRETCH OF UP TO 6.0, AND RESATURATING WITH AN AQUEOUS RESATURATION SOLUTION CONTAINING 3 TO 10 PERCENT SULFURIC ACID AND FROM ABOUT 3 TO 10 PERCENT FORMALDEHYDE AND WHICH IS AT LEAST 90 PERCENT SATURATED WITH SODIUM CHLORIDE 